Heat treatment for titanium base alloy, circa 4% mn, and 4% al



Nov. 1l, 1958 n. J. WEST ETAL 2,360,078 4 HEAT 'l'RETMEN': FOR TITANIUM BASE ALLOY, .CIRCA 4% Mn, AND' 47, A1

Filed May 25. 1955 inval/Elfythe stress.

` the high temperatures. 'i sary to meet 'the specification requirements is a problem confrontingthe entire titanium industry. It is therefore of scrapped titanium articles.

United States Patent HEAT TREATMENT FOR TITANIUM BASE ALLOY, CIRCA 4% Mu, AND 4% Al Donald John West and Richard Augustus Baughman,

Cincinnati, Ohio, assignors to General Electric Company, a corporation of New York Application May `25, 1955, SerialNo. 511,114

6 Claims. (Cl. 148-13) This invention relates to a process for heat' treating titanium 'and in particular'to uaprocess for heat treating a particular'type of titanium alloy inorder. to make it.duc

' tile.

Compressor wheels on a turbojet engine are acritical part of the engine and are subjected Ato high migratory stresses when rotating at high Velocity. Also, large stress concentrations take place when the turbojet engine undergoes sudden bursts of thrust during transient operation. The points of stress concentrations take placerin lareas where there is a tendency for the stresses to build up. tions has ductility, the material can undergo plastic de- If `the material undergoing these stress concentraformationy at the pointof stress concentration and relieve lf the stressconcentration continues to build up and is not relieved, it can result inthe form of an initial fracture -which will later destroy thepart ,and perhaps destroy the engine. This problem becomes particularly critical during the high temperatures and speeds of afjet engine at which time the velocity of rotating parts is also'exceedingly high, so that any-initial fracture .will

vbe seriously aggravated and undoubtedly do a lot of damage to the engine.

Since titanium alloyvhas a` good strength weight ratio, the use of compressor wheels made from titanium alloys is very desirablein order to achieve considerable weight savings in the engine. 'However, one

- ofthe undesirable' features of titanium is that ittends to remain' brittle mainly becauseof the impuritiescontained in the alloy itself or becomes brittle when subjectedto Therefore, the ductility necesa general object of this invention to provide a process for heat treating titanium articles to give them the necessary ductility during engine operating conditions regardless 7 duce a material ductile and stable enough to-allow the manufacture of titanium alloy articles.

Since titanium is a very expensive material, scrapping becomes a very expensive loss. ln general, approximately 50 percent of the compressor wheels made of titanium and heat treated to previous processes, fail to meet the required specifications for ductility'and are rejected. It is therefore another object of this invention to provide a process for heat treating titanium articles to consistently meet the required specification for ductility.

It isy an object of this inventionto provide a process lfor isothermallyheat treating a titanium alloy at various 2860,07@ atented Nov. 11, '8

"dice temperatures in the 'beta kor alpha plus betaphasesand i slowly furnace cooling the alloy at another temperature in the alphaplus lbeta phase without permittingthe''for-l mation of fine 'alpha structure thereby obtaining'improved ductility. u

It is another objectl of this inventionitoheat treat'atitanium alloy consisting of approximately 4 percentmanganese, 4 percent aluminum 'andthe rest titanium and its impurities so as to limpart to'that alloy the necessary fductility `to meet the'required,specifications by' `stabilizing the alloy against age hardening, embrittlement and build-y up of stresses at y'temperatu'resupfto 'about 80.0"" 1'1'- These and Otherobjects will becomemore 'apparent when read in the light of 'the accompanying specification taken in connection with'the attached drawing. `Thescope of myinvention will be pointed out in'the appended claims.

` In general, the invention may be practiced by. heating an alloy comprising about 4%, manganese, about '4% .alu-

minum with the balance essentially titanium'to a temperature just within thebeta range, the area marlced beta in the drawing, or high in the range in which only coarse alpha will form, shown by the shadedv portion in the drawing, maintaining the alloy at this temperature for a period of time, transforming the alloy isothermally to a lower temperature in the range Yin which onlycoarse alpha will form, and then transforming 4the alloy toat vleast one temperature in the alpha plus Vbeta range ,by cooling it slowly, and lastly cooling to room temperature.

The isothermal heat treating'process herein described is similar to that disclosed 'inco-pending patentk'application, Serial No. 5ll,l15,"'iled VMay'25, 195'5, and assigned tothe present assignee of this application. "The process vdiffers however, in that'the alloy as therein described' may be initially heated to a temperature"high wtihin the range in which only coarse'alpha willformto. create as much beta structure as possible instead of heating the alloy completely yto the beta` phase. 'If the process taught by the above-mentioned co-pending application is used with the alloy as herein described, a structure willresult which is not as ductile as that resulting from.

the-heat treatment disclosed by this application.

ln'order to heat treat titanium alloy articles made 'lof approximately 4 percent manganese, 4 percent aluminum and the'rest titanium and-its impurities, .so as to-have the necessaryductility to 'meet .the required spve'ycication, ythe first step is to lbetatize lthe article byheating it to approximately k1720" F.'into the 'area marked bet'a on the drawing. VBetatizing is heat treating 4`the alloy-in the beta field, and we maintain itas low as possibledn 'the beta field so as to form a lbeta structure with al minimum amount of alpha phase before transforming into Vthe alpha plus beta eld. This stabilizingternperature is maintained for approximately 50 minutes. v.By staying at the low temperature in the beta field, :thesmaterial in general will containbeta structure befor'e'transforming back intothe alphaplus .beta structurey atithe i lower temperature.`

The nextl step in the process isthe'risothermal, heat treating portion in which the material-is cooled tofa'pproxV`r imately 1380 F. into the area between theshadedi portion and the beta-{ealpha regions ofthe drawing by jtransferring it to another furnace whichy perhaps -is'already v at the 1380" F. temperature or staying in the furnace'and cooling it down to the 1380" F. temperature. Atthez1380 F. temperature coarse alpha is allowed to formxHowever, if a lsufficiently lower 'temperature than V1380*F. is used,` line alpha structure will be formed. `ltisnoted that the tine alpha structure in the Amaterialcausesfthe brittleness to occur whenfcooling` down-ltotroomtemper t t v 3 ature; It is further noted that if the material is held at a higher temperature than the 13807 F. temperature, less alpha will form in reaching the equilibrium condition so that upon subsequent cooling more fine alpha will be formed thereby causing brittleness. .The stabilizing time `has been found to be approximately 75 minutes. This is Aa minimum time and is critical in order to maintain fan isothermal condition until equilibrium between alpha and the beta phases is established.

After stabilizing the material at V1380 F the material `is thencooled to 1300 F. within the beta-i-alpha region `1"of the drawing for stabilizing at this temperature. This step is necessary since after cooling from the 1380 F. y

` temperature additional alpha may be formed. In other words, at any lower temperature, more alpha is present at equilibrium conditions than at the 1300 F. or l380 F. temperatures. The beta to alpha transformation is a ttime temperature phenomenon. In order to have alpha tand beta in equilibrium at a given temperature, sufficient time for transformation must be allowed. Also, the `lower the temperature, the slower the reaction. Therefore, longer times are required for the 1300 F. temperature than for the l380 F. to allow the alpha and beta phases to reach an equilibrium condition and prevent the v,formation of an unstable beta phase upon subsequent cooling to room temperature. If insuicient time is aljlowed at the 1300 F. temperaturepand unstable beta forms, then a line precipitate will form from the unstable )beta during Subsequent engine operation, thereby causing the loss of ductility of the part. It is therefore necessary to stabilize the material at the 1300 F. temperature fora minimum of two hours.

The next step of the process is to cool the alloy to another temperature in the alpha plus 'beta range which in this instance is approximately 900 F. It is not neces` sary to isothermally heat treat the material at this ternperature, but merely to furnace cool from the 1300 F. temperature to the 900 F. temperature at a slow rate. The material becomes stabilized as it transforms from v theA 1300 F. temperature to the 900 F. temperature.

The last step of the process is to cool the material to room temperature by taking the article out of the furnace. It is noted that cooling down to room temperature by taking the article out of the furnace is much better than to furnace cool since brittleness may result because of furnace cooling thereby making the ductility of the material low.

` Another embodiment of lthe invention has been found in heat treating this titanium alloy to la high temperature in the alpha beta eld without going into the beta field so as to form a large percentage of beta, holding this temperature for a considerable period of time and then furnace cooling'to 'a lower temperature in the alpha plus beta eld, and holding this temperature to stabilize the structure, and then furnace co-oling to a still lower temperature in the alpha beta eld after which the material is air cooled to room temperature. More specifically, the 'alloy is heated to approximately l600 F. for a period of eight hours in order to insure that the material has been stabilized. This stabilizing time is longer than the above referred to method so as to forml suicient beta. In other wordsL/thewstabilizing time is longer. The next step is torfprnace coolto 1300 F. and maintain it at this tem- UV"perature for a period of two hours. The next step is then to furnace cool to 900 F. at a slow rate from the 1300 F. temperature to the 900 F. temperature. It is not necessary to stabilize upon reaching the 900 F. -temperature. After having reached the 900 F. temperature, the material is then air cooled to room temperature.

`The following table which is .a summary of tests conducted on seven different heats of material compares the physical properties of the titanium base alloy containing about.4% manganese and about 4% aluminum before l and after vour novel heat treatment.

4 The marked increase in ductility is especially to be noted:

of titanium alloy after our novel heat treatment process,

l a series of compressor Wheel forgings were aged for up to about 1000 hours. The following table summarizes the results of aging showing the uniform increased ductihty.

Hours at Tensile Percent Aging Temp. F.) Temp. Strength Elongation (p. s. i.) (in 1) Therefore, in order to prevent titanium alloy materials from becoming brittle upon being subjected to relatively high temperatures when in use, the alloy has been heat treated isothermally and stabilized at various temperatures in the beta and alpha plus beta range in order to prevent tine alpha structure from being formed either during the heat treat process or upon being subjected to the high temperatures when being used.

The above example of the invention has been given by way of illustration and is not intended as a limitation of the invention. The times and temperatures given can vary within narrow limits according to the characteristics of the material since it may contain various percentages of impurities or the like. However, such variations are intended to be included within the spirit and scope of this invention since they are regarded as equivalents.

What we claim as new and desired to secure by Letters Patent of the United States is:

l. The process of heat treating a titanium alloy including about 4% manganese and about 4% aluminum comprising heat treating the material to the lowest temperature in the beta range at approximately 1720 F. to form the beta phase and maintaining this temperature until such time as the material becomes betatized, cooling the material to 1380 F. and maintaining this temperature for approximately 75 minutes permitting coarse alpha phase in equilibrium with beta phase to form without permitting ne alpha structure to form, cooling the alloy to 1300 F. and maintaining this temperature for approximately minutes to prevent ne alpha from forming, slowly furnace cooling from 1300 F. to 900 F. to prevent fine alpha from forming, and then air cooling from about 900 F. to room temperature.

2. In a heat treating process for a titanium alloy including about 4% manganese and about 4% aluminum comprising heating the alloy to a temperature inthe beta range for a suicient length of time until the material becomes betatized, cooling to a temperature in the range in which only Icoarse alpha will form and holding this temperature for a su'cient amount of time to permit coarse alpha to form, cooling to a first temperature in the alpha plus beta range and stabilizing the material for a period of time to prevent age hardening, slowly furnace lcoolingfrom the rst temperature in the alpha plus beta range to a second temperature in the alpha plus beta range to prevent fine v alpha from forming, and air cooling this material from prising heating the alloy to a rst temperature in a phase in which only coarse alpha can form but suiiciently high to form beta phase, maintaining this temperature for a suflcient length of time to stabilize the material, cooling to a second temperature in the range in which only coarse alpha can form and maintaining this temperature for a suicient length of time to permit the material to become stabilized, furnace cooling slowly from the last temperature to a temperature in the alpha plus beta range, and then air cooling the material from the temperature in the alpha plus beta range to room temperature.

4. In the process for heat treating a titanium alloy including about 4% manganese and about 4% aluminum comprising heat treating the alloy to 1600 F. for eight hours to permit the material to lbecome stabilized, cooling to 1300 F. and maintaining this temperature for two hours to permit the material to become stabilized, slowly furnace cooling from 1300 F. to 900 F. to prevent fine alpha structure from forming in the material, and air cooling from 900 F. to room temperature.

5. In a process for heat treating an alloy consisting of 4 percent manganese, 4 percent aluminum and the remainder titanium and its impurities comprising heat treating the alloy to 1600 F. for a sufcient length of time for the material to become stabilized, cooling to 1300 F. for a sufcient length of time for the material to become Stabi# lized, slowly furnace cooling from 1300 F. to 900 F., and air cooling from 900 F. to room temperature.

6. In a process for heat treating an alloy consisting of 4 percent manganese, 4 percent aluminum and the remainder titanium and its impurities comprising heat treating the alloy to 1720 F. for a sufficient length of time until the material becomes betatized, cooling the alloy to 1380 F. for a sufficient length of time for the material to become stabilized, cooling the alloy to 1300 F. for a suflicient length of time for the material to become stabilized, slowly furnace cooling the alloy to 900 F., and air cooling the alloy from 900 F. to room temperature.

Atlas of Isothermal Tranformations, U. S. Steel, pages 6-26, 1951. 

2. IN A HEAT TREATING PROCESS FOR A TITANIUM ALLOY INCLUDING ABOUT 4% MANGANESE AND ABOUT 4% ALUMINUM COMPRISING HEATING THE ALLOY TO A TEMPERATURE IN THE BETA RANGE FOR A SUFFICIENT LENGTH OF TIME UNTIL THE MATERIAL BECOMES BETALIZED, COOLING TO A TEMPERATURE IN THE RANGE IN WHICH ONLY COURSE ALPHA WILL FORM AND HOLDING THIS TEMPERATURE FOR A SUFFICIENT AMOUNT OF TIME TO PERMIT COARSE ALPHA TO FORM, COOLING TO A FIRST TEMPERATURE IN THE ALPHA PLUS BETA RANGE AND STABILIZING THE MATERIAL FOR A PERIOD OF TIME TO PREVENT AGE HARDENING, SLOWLY FURNACE COOLING FROM THE FIRST TEMPERATURE IN THE ALPHA PLUS BETA RANGE TO A SECOND TEMPERATURE IN THE ALPHA PLUS BETA RANGE TO PREVENT FINE ALPHA FRO FORMING AND AIR COOLING THIS MATERIAL FROM THE SECOND TEMPERATURE IN THE ALPHA PLUS BETA RANGE TO ROOM TEMPERATURE. 